Guys.......I am running a 67 440 HP that is .060 over in my 67 GTX. The only modifcations to the engine are a 6-pack cam and a good valve job on stock heads. It has the stock 4327s Carter AFB. The jetting is stock: primaries @ .098 and secondaries @ .077 I'm running stock 3:23 gears and a 727 auto transmission. Does anyone know how big I can goto on the secondary jets for more top end power without affecting basic drivabilty ?

That seems to small for stock jetting There normally around 10 to 13 thousands (.010 to.013)smaller on the hole size on the secondary jets stock. I would put a .086 jet in both sides and see how that works, if you like it try a .089 and on up until it quits making more power. Is your intake manifold stock? If so what casting number is it? I'm not sure when Mopar went to the bigger Carter AVS on the Hi-Po 440 magnum motors, I thought it was 1967 Are your primary butterflys the same size aas the secondarys ones? If not it may not be the correct carb. for your motor I have some old Carter catalogs, I'll look in them and see if I can find your carb. # and the stock jetting for it, if so I'll add it onto here later this morning Edited, no luck on the jet sizes, sorry

The carter 4327 is a 750cfm unit. I'd suggest you beg, borrow, steal, or buy a LM-2 or similar A/F meter before playing with the carb.Dave

Ma Mopar use to have recommended jetting and other carb mods. For the 4326 and 27's the primarys were .104" and secondarys .083 (left) and .089 (right) with metering rods 164 and 161 rspectively. this was on a CH4B. FWIW.

I made similar changes to my stock engine/carb on a cast iron manifold and I recall that at the time I believed that it lowered my et. However, my data collection and consistancy was not that robust at that time. I also lightened the counter weight for the secondarys. I believed that that made a bigger difference than the jetting.

I believe Chrysler went to the AVS carb in 68 or 69. The 4327s is correct carb for the 67 GTX & Dodge RT with the HP 440 & A/T. The secondary openings are larger than the primaries. I am using the stock cast iron intake manifold #2086178. Years ago I read somewhere that the 4327s and 4326s(for 4-speed cars) were not providing enough gas on the top end. The stock 440 HP could handle more. The simple fix was to use larger secondary jets. I cannot find the article or remember the size jets to install. I agree with your advise to try .089 for a start.

The correct answer is that there is no correct answer. Every engine combo and a host of other factors (elevation, weatheretc.) will vary the results.

As mentioned above, experimenting on your engine using a selection of jets and rods along with an LM2, Air fuel meter, dyno, etc. will show you your best combo.

One thing that you might find suprising is that the factory jetting was pretty darn flexible, you may find that the best power is made with the stock combo or some combo really close to it.